Method for transmitting V2X signal of terminal having limited transmission capability and terminal using the method

ABSTRACT

Provided are a method for transmitting a vehicle-to-everything (V2X) signal performed by a user equipment (UE) having a limited transmission capability in a multi-carrier system and a UE using the method. The method includes selecting a first resource in a first carrier, if using a specific subframe in a second carrier exceeds a transmission capability of the UE considering the first resource, selecting a second resource randomly among the remaining subframes except the specific subframe in the second carrier and transmitting the V2X signal using the first resource and the second resource.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Applications No.62/505,850 filed on May 13, 2017, No. 62/544,762 filed on Aug. 11, 2017,No. 62/571,170 filed on Oct. 11, 2017, No. 62/570,115 filed on Oct. 10,2017, No. 62/571,281 filed on Oct. 12, 2017, No. 62/588,136 filed onNov. 17, 2017, No. 62/631,493 filed on Feb. 15, 2018, priority of KoreanPatent Application No. 10-2018-0029347 filed on Mar. 13, 2018, andpriority of Korean Patent Application No. 10-2018-0053130 filed on May9, 2018, the contents of which are all hereby incorporated by referenceherein in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to wireless communications, and moreparticularly, to a method for a terminal having limited transmissioncapability to transmit V2X signals and a terminal using the method.

Background Art

There is a growing interest in a Device-to-Device (D22) technology inwhich devices perform direct communication. In particular, D2D has beenin the spotlight as a communication technology for a public safetynetwork. The public safety network has higher service requirements(reliability and security) than the commercial communication network. Inparticular, if coverage of cellular communication is not affected oravailable, the public safety network also requires direct communicationbetween devices, that is, D2D operation.

D2D operation may have various advantages in that it is communicationbetween devices in proximity. For example, D2D UE has a high transferrate and a low delay and may perform data communication. Furthermore, inD2D operation, traffic concentrated on a base station can bedistributed. If D2D UE plays the role of a relay, it may also play therole of extending coverage of a base station.

Meanwhile, in long term evolution-advanced (LTE-A), an interface betweena terminal and a terminal is referred to as sidelink, and the sidelinkmay also be used for a communication between terminals installed onvehicles or between a terminal installed on a vehicle and anotherarbitrary terminal, that is, vehicle-to-everything (V2X) communication.

The conventional V2X communication does not support the carrieraggregation. The carrier aggregation means that carriers can be used incombination, and is classified into an aggregation of contiguouscarriers and an aggregation of non-contiguous carriers.

When the carrier aggregation is used in the V2X communication, aterminal may transmit V2X signals by using a plurality of carriers.However, a terminal is not always able to transmit V2X signalssimultaneously in all carriers that are configured. For example, in thecase that the number of transmission chains that are provided is lessthan the number of carriers that are configured, the terminal is notable to support the transmission of V2X signals simultaneously in all ofthe configured carriers.

In the case that the carrier aggregation is used for the V2Xcommunication with respect to the terminal that has such a limitedtransmission capability, it becomes a problem the way of selecting atransport resource by the terminal.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method fortransmitting a V2X signal by a terminal that has a limited transmissioncapability in a multi-carrier system and a terminal using the method.

In one aspect, provided is a method for transmitting avehicle-to-everything (V2X) signal performed by a user equipment (UE)having a limited transmission capability in a multi-carrier system. Themethod includes selecting a first resource in a first carrier, if usinga specific subframe in a second carrier exceeds a transmissioncapability of the UE considering the first resource, selecting a secondresource randomly among the remaining subframes except the specificsubframe in the second carrier and transmitting the V2X signal using thefirst resource and the second resource.

A number of transmission chains for the UE may be smaller than a numberof configured transmission carriers in the specific subframe.

The UE may not support a frequency band combination including the firstresource of the first carrier and the second resource of the secondcarrier.

The specific subframe may correspond to a transmission chain switchingtime of the UE.

The method may further include receiving V2X configuration information.The V2X configuration information may indicate that a transmissionresource is selected in an order of the first carrier and the secondcarrier.

The UE may select a transmission resource in an order of the firstcarrier and the second carrier based on a channel busy ratio (CBR) and aProSe priority per packet (PPPP) of the V2X signal.

The first carrier and the second carrier may be configured to the UE bycarrier aggregation.

In another aspect, provided is a user equipment (UE). The UE includes atransceiver configured to transmit and receive a radio signal and aprocessor operated in connection with the transceiver. The processorselects a first resource in a first carrier, when a specific subframeused in a second carrier exceeds a transmission capability of the UEconsidering the first resource, selects a second resource randomly amongthe remaining subframes except the specific subframe in the secondcarrier and transmits the V2X signal using the first resource and thesecond resource.

According to the present invention, when the carrier aggregation is usedin a V2X communication, a transmission resource is selected efficientlyon a plurality of carriers by considering a transmission capability of aterminal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless communication system.

FIG. 2 is a diagram showing a wireless protocol architecture for a userplane.

FIG. 3 is a diagram showing a wireless protocol architecture for acontrol plane.

FIG. 4 illustrates scenarios for a V2X communication.

FIG. 5 illustrates an SLSS resource configuration method according to anembodiment of the present invention.

FIG. 6 illustrates an SLSS transmission method according to the presentinvention.

FIG. 7 illustrates a particular example to which the method described inFIGS. 5 and 6 is applied.

FIG. 8 illustrates an example (option 1-1) of resource selection foreach carrier in the case that the carrier aggregation is used in V2Xtransmission.

FIG. 9 illustrates a resource selection method performed by a UEaccording to option 1-1 described above.

FIG. 10 illustrates another example (option 1-2) of a resource selectionfor each carrier in the case that the carrier aggregation is used in V2Xcommunication.

FIG. 11 illustrates another example (option 2) of a resource selectionfor each carrier in the case that the carrier aggregation is used in V2Xcommunication.

FIG. 12 illustrates an example of a resource selection in the case thatthe CA is applied in sidelink.

FIG. 13 is a block diagram of an apparatus in which the embodiment ofthe present invention is implemented.

FIG. 14 illustrates an example of configuring a processor 1100.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 shows a wireless communication system.

The wireless communication system may be referred to as an Evolved-UMTSTerrestrial Radio Access Network (E-UTRAN) or a Long Term Evolution(LTE)/LTE-A system, for example.

The E-UTRAN includes at least one base station (BS) 20 which provides acontrol plane and a user plane to a user equipment (UE) 10. The UE 10may be fixed or mobile, and may be referred to as another terminology,such as a mobile station (MS), a user terminal (UT), a subscriberstation (SS), a mobile terminal (MT), a wireless device, etc. The BS 20is generally a fixed station that communicates with the UE 10 and may bereferred to as another terminology, such as an evolved node-B (eNB), abase transceiver system (BTS), an access point, etc.

The BSs 20 are interconnected by means of an X2 interface. The BSs 20are also connected by means of an S1 interface to an evolved packet core(EPC) 30, more specifically, to a mobility management entity (MME)through S1-MME and to a serving gateway (S-GW) through S1-U.

The EPC 30 includes an MME, an S-GW, and a packet data network-gateway(P-GW). The MME has access information of the UE or capabilityinformation of the UE, and such information is generally used formobility management of the UE. The S-GW is a gateway having an E-UTRANas an end point. The P-GW is a gateway having a PDN as an end point.

Layers of a radio interface protocol between the UE and the network canbe classified into a first layer (L1), a second layer (L2), and a thirdlayer (L3) based on the lower three layers of the open systeminterconnection (OSI) model that is well-known in the communicationsystem. Among them, a physical (PHY) layer belonging to the first layerprovides an information transfer service by using a physical channel,and a radio resource control (RRC) layer belonging to the third layerserves to control a radio resource between the UE and the network. Forthis, the RRC layer exchanges an RRC message between the UE and the BS.

A wireless communication system may be a time division duplex (TDD)system, a frequency division duplex (FDD) system or a system in whichthe TDD and the FDD are used in mixed manner.

FIG. 2 is a diagram showing a wireless protocol architecture for a userplane. FIG. 3 is a diagram showing a wireless protocol architecture fora control plane. The user plane is a protocol stack for user datatransmission. The control plane is a protocol stack for control signaltransmission.

Referring to FIGS. 2 and 3, a PHY layer provides an upper layer with aninformation transfer service through a physical channel. The PHY layeris connected to a medium access control (MAC) layer which is an upperlayer of the PHY layer through a transport channel Data is transferredbetween the MAC layer and the PHY layer through the transport channel.The transport channel is classified according to how and with whatcharacteristics data is transferred through a radio interface.

Data is moved between different PHY layers, that is, the PHY layers of atransmitter and a receiver, through a physical channel. The physicalchannel may be modulated according to an Orthogonal Frequency DivisionMultiplexing (OFDM) scheme, and use the time and frequency as radioresources.

The functions of the MAC layer include mapping between a logical channeland a transport channel and multiplexing and demultiplexing to atransport block that is provided through a physical channel on thetransport channel of a MAC Service Data Unit (SDU) that belongs to alogical channel. The MAC layer provides service to a Radio Link Control(RLC) layer through the logical channel.

The functions of the RLC layer include the concatenation, segmentation,and reassembly of an RLC SDU. In order to guarantee various types ofQuality of Service (QoS) required by a Radio Bearer (RB), the RLC layerprovides three types of operation mode: Transparent Mode (TM),Unacknowledged Mode (UM), and Acknowledged Mode (AM). AM RLC provideserror correction through an Automatic Repeat Request (ARQ).

The RRC layer is defined only on the control plane. The RRC layer isrelated to the configuration, reconfiguration, and release of radiobearers, and is responsible for control of logical channels, transportchannels, and PHY channels. An RB means a logical route that is providedby the first layer (PHY layer) and the second layers (MAC layer, the RLClayer, and the PDCP layer) in order to transfer data between UE and anetwork.

The function of a Packet Data Convergence Protocol (PDCP) layer on theuser plane includes the transfer of user data and header compression andciphering. The function of the PDCP layer on the user plane furtherincludes the transfer and encryption/integrity protection of controlplane data.

What an RB is configured means a process of defining the characteristicsof a wireless protocol layer and channels in order to provide specificservice and configuring each detailed parameter and operating method. AnRB can be divided into two types of a Signaling RB (SRB) and a Data RB(DRB). The SRB is used as a passage through which an RRC message istransmitted on the control plane, and the DRB is used as a passagethrough which user data is transmitted on the user plane.

If RRC connection is established between the RRC layer of UE and the RRClayer of an E-UTRAN, the UE is in the RRC connected state. If not, theUE is in the RRC idle state.

A downlink transport channel through which data is transmitted from anetwork to UE includes a broadcast channel (BCH) through which systeminformation is transmitted and a downlink shared channel (SCH) throughwhich user traffic or control messages are transmitted. Traffic or acontrol message for downlink multicast or broadcast service may betransmitted through the downlink SCH, or may be transmitted through anadditional downlink multicast channel (MCH). Meanwhile, an uplinktransport channel through which data is transmitted from UE to a networkincludes a random access channel (RACH) through which an initial controlmessage is transmitted and an uplink shared channel (SCH) through whichuser traffic or control messages are transmitted.

Logical channels that are placed over the transport channel and that aremapped to the transport channel include a broadcast control channel(BCCH), a paging control channel (PCCH), a common control channel(CCCH), a multicast control channel (MCCH), and a multicast trafficchannel (MTCH).

The physical channel includes several OFDM symbols in the time domainand several subcarriers in the frequency domain. One subframe includes aplurality of OFDM symbols in the time domain. An RB is a resourcesallocation unit, and includes a plurality of OFDM symbols and aplurality of subcarriers. Furthermore, each subframe may use specificsubcarriers of specific OFDM symbols (e.g., the first OFDM symbol) ofthe corresponding subframe for a physical downlink control channel(PDCCH), that is, an L1/L2 control channel A Transmission Time Interval(TTI) is a unit time for subframe transmission.

The RRC state means whether or not the RRC layer of UE is logicallyconnected to the RRC layer of the E-UTRAN. A case where the RRC layer ofUE is logically connected to the RRC layer of the E-UTRAN is referred toas an RRC connected state. A case where the RRC layer of UE is notlogically connected to the RRC layer of the E-UTRAN is referred to as anRRC idle state. The E-UTRAN may check the existence of corresponding UEin the RRC connected state in each cell because the UE has RRCconnection, so the UE may be effectively controlled. In contrast, theE-UTRAN is unable to check UE in the RRC idle state, and a Core Network(CN) manages UE in the RRC idle state in each tracking area, that is,the unit of an area greater than a cell. That is, the existence ornon-existence of UE in the RRC idle state is checked only for each largearea. Accordingly, the UE needs to shift to the RRC connected state inorder to be provided with common mobile communication service, such asvoice or data.

When a user first powers UE, the UE first searches for a proper cell andremains in the RRC idle state in the corresponding cell. The UE in theRRC idle state establishes RRC connection with an E-UTRAN through an RRCconnection procedure when it is necessary to set up the RRC connection,and shifts to the RRC connected state. A case where UE in the RRC idlestate needs to set up RRC connection includes several cases. Forexample, the cases may include a need to send uplink data for a reason,such as a call attempt by a user, and to send a response message as aresponse to a paging message received from an E-UTRAN.

A Non-Access Stratum (NAS) layer placed over the RRC layer performsfunctions, such as session management and mobility management.

In the NAS layer, in order to manage the mobility of UE, two types ofstates: EPS Mobility Management-REGISTERED (EMM-REGISTERED) andEMM-DEREGISTERED are defined. The two states are applied to UE and theMME. UE is initially in the EMM-DEREGISTERED state. In order to access anetwork, the UE performs a process of registering it with thecorresponding network through an initial attach procedure. If the attachprocedure is successfully performed, the UE and the MME become theEMM-REGISTERED state.

In order to manage signaling connection between UE and the EPC, twotypes of states: an EPS Connection Management (ECM)-IDLE state and anECM-CONNECTED state are defined. The two states are applied to UE andthe MME. When the UE in the ECM-IDLE state establishes RRC connectionwith the E-UTRAN, the UE becomes the ECM-CONNECTED state. The MME in theECM-IDLE state becomes the ECM-CONNECTED state when it establishes S1connection with the E-UTRAN. When the UE is in the ECM-IDLE state, theE-UTRAN does not have information about the context of the UE.Accordingly, the UE in the ECM-IDLE state performs procedures related toUE-based mobility, such as cell selection or cell reselection, without aneed to receive a command from a network. In contrast, when the UE is inthe ECM-CONNECTED state, the mobility of the UE is managed in responseto a command from a network. If the location of the UE in the ECM-IDLEstate is different from a location known to the network, the UE informsthe network of its corresponding location through a tracking area updateprocedure.

Now, the D2D operation will now be described. In 3GPP LTE-A, the servicerelated to D2D operation is called proximity based service (ProSe).Hereinafter, ProSe is equivalent to D2D operation and ProSe may beinterchanged with D2D operation. ProSe will now be described.

The ProSe includes ProSe direction communication and ProSe directdiscovery. The ProSe direct communication is communication performedbetween two or more proximate UEs. The UEs may perform communication byusing a protocol of a user plane. A ProSe-enabled UE implies a UEsupporting a procedure related to a requirement of the ProSe. Unlessotherwise specified, the ProSe-enabled UE includes both of a publicsafety UE and a non-public safety UE. The public safety UE is a UEsupporting both of a function specified for a public safety and a ProSeprocedure, and the non-public safety UE is a UE supporting the ProSeprocedure and not supporting the function specified for the publicsafety.

ProSe direct discovery is a process for discovering anotherProSe-enabled UE adjacent to ProSe-enabled UE. In this case, only thecapabilities of the two types of ProSe-enabled UE are used. EPC-levelProSe discovery means a process for determining, by an EPC, whether thetwo types of ProSe-enabled UE are in proximity and notifying the twotypes of ProSe-enabled UE of the proximity.

Hereinafter, for convenience, the ProSe direct communication may bereferred to as D2D communication, and the ProSe direct discovery may bereferred to as D2D discovery. The link used for a D2D operation isreferred to as sidelink in LTE.

Now, a vehicle to everything (V2X) communication is described. The V2Xmeans a communication between a UE installed on a vehicle and anotherUE, and another UE may correspond to a pedestrian, a vehicle or aninfrastructure. In this case, these may be referred to as a vehicle topedestrian (V2P), a vehicle to vehicle (V2V) and a vehicle toinfrastructure (V2I), respectively.

The V2X communication transmits/receives data/control informationthrough sidelink defined in a D2D operation, not through uplink/downlinkbetween an eNB and a UE, which is used in the conventional LTEcommunication.

The following physical channels may be defined in sidelink as below.

Physical Sidelink Broadcast CHannel (PSBCH) is a physical sideleinkbroadcast channel. Physical Sidelink Control CHannel (PSCCH) is aphysical sidelink control channel. Physical Sidelink Discovery CHannelis a physical sidelink discovery channel.

Physical Sidelink Shared CHannel is a physical sidelink shared channel.Sidelink Synchronization Signal (SLSS) is a sidelink synchronizationsignal. The SLSS may include Primary Sidelink Synchronization Signal(PSSS) and Secondary Sidelink Synchronization Signal (SSSS). The SLSSand the PSBCH may be transmitted together.

The sidelink may mean an interface between a UE and a UE, and thesidelink may correspond to PC5 interface.

FIG. 4 illustrates scenarios for a V2X communication.

Referring to FIG. 4(a), a V2X communication may support an informationexchange operation (between UEs) based on PC5, which is an interfacebetween UEs, and as shown in FIG. 4(b), may also support an informationexchange operation (between UEs) based on Uu, which is an interfacebetween an eNodeB and a UE. In addition, as shown in FIG. 4(c), aninformation exchange operation (between UEs) maybe supported by usingboth of the PC5 and the Uu.

Hereinafter, for the convenience of description, the present inventionis described based on a 3GPP LTE/LTE-A system. However, the scope of thesystem to which the present invention is applied is extendable to othersystem in addition to the 3GPP LTE/LTE-A system.

Now, the present invention is described.

The technical proposals below propose a method for a UE that has nocapability of performing a simultaneous transmission and/or reception(or a UE that has a limitation in a capability of a simultaneoustransmission and/or reception, and hereinafter, such a UE is referred toas ‘LCAP_UE’) to perform a V2X communication efficiently on a pluralityof (V2X) carriers which are configured (/signaled) in the CarrierAggregation (CA) technique.

(A part of) The technical proposals of the present invention may belimitedly applied under a situation of “contiguous or non-contiguous CAin Intra-B and”.

V2X communication modes include (A) a mode (this is referred to as mode#3) in which an eNB signals (/controls) scheduling information inrelation to V2X message transmission (/reception) (on V2X resource poolwhich is preconfigured (/signaled) (from an eNB (/network))(representatively). In mode 3, for example, a UE located in eNBcommunication coverage (and/or in RRC_CONNECTED state) is a main target.And/or the V2X communication modes include (B) a mode (this is referredto as mode #4) in which a UE independently determines (/controls)scheduling information in relation to V2X message transmission(/reception) (on V2X resource pool which is preconfigured(/signaled)(from an eNB (/network)). In mode 3, for example, a UElocated in/out of eNB communication coverage (and/or inRRC_CONNECTED/RRC_IDEL states) may be a main target.

In the present invention, “sensing operation” may be interpreted asPSSCH-RSRP measurement operation based on PSSCH DM-RS sequence which isscheduled by a PSCCH in which decoding is successful and/or S-RSSImeasurement operation based on a sub channel in relation to V2X resourcepool.

In the present invention, “reception” may be extendedly interpreted asat least one of:

(A) V2X channel (/signal) (e.g., PSCCH, PSSCH, PSBCH, PSSS/SSSS, etc.)decoding (/reception) operation (and/or WAN DL channel (/signal) (e.g.,PDCCH, PDSCH, PSS/SSS, etc.) decoding (/reception) operation,

(B) Sensing operation, and

(C) CBR measurement operation.

In the present invention, “transmission” may be extendedly interpretedas V2X channel (/signal) (e.g., PSCCH, PSSCH, PSBCH, PSSS/SSSS, etc.)transmission operation (and/or WAN UL channel (/signal) (e.g., PUSCH,PUCCH, SRS, etc.) transmission operation).

In the present invention, “carrier” may be extendedly interpreted as atleast one of (A) carrier set (/group) which is configured (/signaled) inadvance, (B) V2X resource pool (set (/group)), and (C) time/frequencyresource set/group on a carrier.

(A part of) the technical proposals of the present invention may beextendedly applied to a V2X communication of a UE (e.g., a UE havingsimultaneous transmission and/or reception capability on a plurality of(V2X) carriers that are preconfigured (/signaled) by the CA, of whichcapability is relatively better than an LCAP_UE).

In the present invention, “synchronization signal” may be extendedlyinterpreted as it includes “PSBCH” as well as “SLSS”. In the presentinvention, “LCAP_UE” may be extendedly interpreted as at least one of aUE having “limited transmission (chain) capability” and a UE having“limited reception (chain) capability”.

Sidelink Received Signal Strength Indicator (S-RSSI), Sidelink ReferenceSignal Received Power (S-RSRP), Channel busy ratio (CBR) and Channeloccupancy ratio (CR) will be described.

First, the S-RSSI is an indicator of reception signal strength insidelink. The S-RSSI may be defined as a linear average of totalreception power for each SC-FDMA symbol in SC-FDMA symbols #1, 2, . . ., 6 of the first slot and SC-FDMA symbols #0, 1, . . . , 5 of asubframe, that a UE observes in a sub channel which is configured.

The S-RSRP means a reception power of a reference signal in sidelink. Inthe S-RSRP, for example, there is PSSCH-RSRP in which RSRP is calculatedin a PSSCH. The PSSCH-RSRP may be defined as a linear average of powercontributions of resource elements (REs) that carry a demodulationreference signal (DM-RS) associated with a PSSCH in physical resourceblocks (PRBs) that are indicated by an associated PSCCH.

The CBR indicates a busy ratio of a channel, and the CBR measured insubframe n may be defined as below.

The PSSCH is sensed in subframe [n−100, n−1], and indicates a ratio in aresource pool of a sub channel that has an S-RSSI which is measured asexceeding a predefined or preconfigured threshold.

The PSCCH is sensed in subframe [n−100, n−1], and indicates a ratio ofresources of a PSCCH pool that has an S-RSSI which is measured asexceeding a predefined or preconfigured threshold in a pool configuredsuch that a PSCCH is transmitted together with the corresponding PSSCHin non-contiguous resource blocks. Here, it is assumed that the PSCCHpool includes resources of a size of two consecutive PRB pairs in afrequency domain.

The CR means a channel occupation rate. The CR calculated in subframe nmay be defined as a value total summation of the number of sub channelsused for a transmission of itself in subframe [n−a, n−1] and the numberof sub channels allowed for a transmission of itself in subframe [n,n+b] divided by the number of sub channels configured in a transmissionpool throughout subframe [n−a, n+b].

Here, ‘a’ is a positive integer and b is 0 or a positive integer. ‘a’and ‘b’ are determined by a UE. ‘a’ and ‘b’ are in a relation ofa+b+1=1000 and a is 500 or more, and n+b should not exceed the latesttransmission opportunity of a grant for a current transmission.

[Proposed method #1] Among a plurality of V2X carriers that areconfigured (/signaled) by the CA, an LCAP_UE may perform a transmission(and/or reception) operation preferentially, on a carrier is selectedaccording to (a part of) priority information (/rule) which isconfigured (/signaled) in advance.

(Rule #1-1) (A) Transmission (and/or reception) carrier in relation to aspecific service (and/or data (/message (/application type))) which ispreconfigured (/signaled) and/or (B) Carrier on which V2X messagetransmission (and/or reception) operation is performed based on PPPP(and/or (remaining) LATENCY REQUIREMENT) and/or message generation(/transmission (/reception))) Period which is greater (or smaller) thana threshold value))) which is preconfigured (/signaled) (and/orrelatively greater (or smaller) and/or resource reservation interval(/period) and/or (C) Transmission (and/or reception) carrier and/or (D)Carrier in which a simultaneous signal transmission (and/or reception)is configured (/signaled) (and/or (time/frequency) synchronizationreference carrier in relation to V2X transmission (and/or reception) onother carrier and/or (E) Carrier in which a (specific) SYNCH SOURCE TYPEwhich is preconfigured (/signaled) has (relatively) higher priority (F)Scheduling (and/or scheduled) carrier in the case that CROSS-CARRIERSCHEDULING (CCS) is configured (/signaled) and/or (G) Transmission(and/or reception) carrier having CBR (/CR) measurement value which isgreater (or smaller) than a threshold value which is preconfigured(/signaled)(and/or relatively greater (or smaller)) (and/or (remaining)CR_LIMIT and/or (maximum) (allowed) transmission power) and/or (H)Carrier of higher (or lower) priority which is preconfigured (/signaled)and/or (I) Shared carrier (with WAN (uplink) communication).

(Rule #1-2) In the (Rule #1-1), at least one information of(representative) CBR, CR, (remaining) CR_LIMIT and (maximum allowed)transmission power of a carrier which is used as a carrier (priority)selection criteria may be derived (/defined) as an (weighted) averagevalue of a plurality of (transmission/reception) resource pool related(measurement/configuration) values on a carrier or a maximum value(/minimum value).

As another example, after a carrier is selected based on the (priority)rule described above, among a plurality of (transmission/reception)resource pools on the corresponding carrier which is selected, thecriteria (/priority parameter) described above may be (re)applied to aselection of (transmission/reception) pool which is going to be used forV2X message transmission (/reception) actually.

[Proposed method #2] For each carrier, at least one of resource location(/pattern), period and subframe offset information to which atransmission (and/or reception) operation is preferentially performed incomparison with other carrier may be preconfigured or signaled.

As an example, when an LCAP_UE performs at least one of (A)(transmission) resource reservation (/selection) operation, (B) sensingoperation (e.g., S-RSSI measurement, PSSCH-RSRP measurement), and (C)CBR measurement operation, the (only) corresponding configuration(/signaling) may used preferentially.

For another example, since the synchronization signal transmission(and/or reception) operation is relatively important for maintaining V2Xcommunication performance, a resource on carrier # Y (partially)overlapped with synchronization signal transmission (and/or reception)resource on carrier # X may not perform sensing operation and/or CBRmeasurement operation and/or (transmission) resource reservation(/selection) operation and/or V2X message (/channel/signal) transmission(/reception).

As an example, by allocating (/signaling) a specific (virtual) PPPP(P_SYN) (in advance), that of PPPP which is relatively lower than theP_SYN may be omitted during protecting the corresponding synchronizationsignal reception (/transmission) operation (e.g., V2X message(/channel/signal) reception (/transmission) which is (partially)overlapped with synchronization signal reception (/transmission)resource).

For another example, in order to alleviate synchronization signaltransmission power decrease, in the resource on carrier # Y which is(partially) overlapped with the synchronization signal transmissionresource on carrier # X, (A) a transmission operation in relation to aspecific service (and/or data (/message (/application) type)) which ispreconfigured (/signaled) and/or (B) PPPP greater (or smaller) than athreshold value which is preconfigured (/signaled) (e.g., it may beinterpreted that (virtual) PPP of the (corresponding) threshold valuewhich is preconfigured (/signaled) (or specific (virtual) PPPP)) may beperformed (/allowed) (and/or (remaining) delay requirement and/ormessage generation (/transmission (/reception)) period and/or resourcereservation interval (/period) based V2X message transmission operationonly may be performed (/allowed).

[Proposed method #3] In the case that V2X message transmission operationis performed on subframe (SF) # K timing of carrier # A based on the[Proposed method #1] and/or [Proposed method #2] described above, and itis unable to monitor (and/or sense) SF # P of carrier # B which is(partially or entirely) overlapped with the corresponding subframe(i.e., SF # K of carrier A) on a time domain, an LCAP_UE may exclude(all of) candidate (transmission) resources (in a selection window) thatmay be overlapped (or collided) with a resource which is separated asmuch as (candidate) resource reservation period once (and/orpreconfigured (/signaled) count) from SF # P, when reserving(/selecting) V2X communication related (transmission) resource oncarrier # B.

[Proposed method #4] By synchronizing the following (partial) parameters(/configuration) between multiple carriers that are preconfigured(/signaled), an LCAP_UE (or UE) may perform V2X communicationefficiently on a plurality of (V2X) carriers which is configured(/signaled) by the CA.

(Rule #4-1) A transmission (and/or reception) resource location (and/or)the number of a synchronization signal (SLSS) (and/or subframe locationin relation to V2X resource pool and/or the number (and/or sub channelsize and/or the number) may be synchronized among multiple carriers.

In the case that the rule is applied, between the multiple carriers,(sidelink) logical (subframe) index (and/or DFN) (and/or V2X resourcepool) in relation to V2X communication may be synchronized (based onANCHOR CARRIER or synchronization based carrier), and through this, theproblem of unable to perform simultaneous transmission and/or receptionon multiple (V2X) carriers that are configured (/signaled) by the CA maybe solved efficiently. In other words, on multiple carriers,simultaneous transmission (or reception) operation may be efficientlyscheduled (/performed).

FIG. 5 illustrates an SLSS resource configuration method according to anembodiment of the present invention.

Referring to FIG. 5, with respect to V2X communication, three carriers(carriers #1, 2 and 3) may be configured to a UE by the carrieraggregation.

In this case, the number and the location of SLSS resources may beidentically configured between multiple carriers. As shown in FIG. 5, incarriers #1, 2 and 3, the number and the location of configured SLSSresources are identical. The reason of this configuration is designedfor setting (sidelink) logical (subframe) indexes (and/or Direct Framenumber (DFN)) in relation to V2X communication to be identical in thecarriers #1, 2 and 3. That is, the frames overlapped in a time domain incarriers #1, 2 and 3 may have the same (sidelink) logical (subframe)index (and/or DFN) value.

In the aspect of a UE, the UE may assume that the location and thenumber of SLSS resources are identical in all carriers that areaggregated for V2X communication.

As an example, the carrier (pair) in which the parameters(/configuration) described above are identical (and/or to which thecross carrier scheduling is configured (/signaled) and/or the carrier(pair) that has an identical (time/frequency) synchronization referencecarrier) may be (limitedly) configured (/signaled) among (A) a(transmission and/or reception) carrier in relation to (specific) anidentical service (and/or data (/message (/application)) type)(preconfigured (/signaled)) and/or (B) a (transmission and/or reception)carrier in which a (specific) an identical synchronization source type(preconfigured (/signaled)) has (relatively) higher priority and/or (C)a carrier (pair) to which CCS is configured (/signaled) and/or a carrier(pair) of which (time/frequency) synchronization difference is smallerthan a preconfigured (/signaled) threshold value and/or a (transmissionand/or reception) carrier that has (specific) an identical(time/frequency) synchronization reference carrier (preconfigured(/signaled)) and/or a transmission (and/or reception) carrier and/or acarrier to which synchronization signal transmission (and/or reception)is configured (/signaled) and/or a (time/frequency) synchronizationreference carrier in relation to V2X transmission (and/or reception) ondifferent carriers.

(Rule #4-2) As an example, in the case of the carrier to which anidentical (time/frequency) synchronization reference carrier isconfigured (/signaled) (this is referred to as a carrier which is not asynchronization reference carrier, and called NON-SYNRFCC), forsupporting V2X communication of the existing (LEGACY) UE (e.g., UEoperating in accordance with LTE REL-14) on the (corresponding) carrierwhich is not a synchronization reference carrier (NON-SYNRFCC), asynchronization resource may be configured (/signaled).

As another example, a synchronization resource configuration(/signaling) on the (corresponding) carrier which is not asynchronization reference carrier (non-synchronization referencecarrier; NON-SYNRFCC) may be performed for the purpose of synchronizing(sidelink) logical (subframe) indexes (and/or DFN) between asynchronization reference carrier and a non-synchronization referencecarrier. For this, the location (/number) of a synchronization resourceconfigured (/signaled) on the non-synchronization reference carrier maybe identical to that of the synchronization reference carrier.Alternatively, it may be implemented that the synchronization resourceconfigured (/signaled) on the non-synchronization reference carrier isvalid only in the case that the synchronization resource is configured(/signaled) on the synchronization reference carrier.

As an example, in the case of an improved UE (UE operating in accordancewith LTE REL-15), according to a network configuration (/signaling), atransmission operation of a synchronization signal (e.g., SLSS) may beperformed on a synchronization resource on the non-synchronizationreference carrier (NON-SYNRFCC) (as well as the synchronizationreference carrier). In this case, even in the case that asynchronization resource is configured on the non-synchronizationreference carrier (and/or the synchronization reference carrier), it maybe interpreted that a network (finally) instructs (/controls) whether totransmit actual synchronization signal of the improved UE. For example,in the case that a synchronization resource is configured on thesynchronization reference carrier, an SLSS may be transmitted in alltimes by using the synchronization resource. On the contrary, even inthe case that a synchronization resource is configured on thenon-synchronization reference carrier, a network may control whether totransmit a synchronization signal actually.

The non-synchronization reference carrier on which the (identical)(time/frequency) synchronization reference carrier is configured(/signaled) may be restricted to a (transmission and/or reception)carrier that an identical synchronization source type has (relatively)higher priority than the synchronization reference carrier.

FIG. 6 illustrates an SLSS transmission method according to the presentinvention.

Referring to FIG. 6, a UE receives SLSS resource configurationinformation, but the SLSS resource configuration information mayconfigure SLSS resources of the same location and number in each ofmultiple carriers that are carrier-aggregated (step, S210). As describedabove with reference to FIG. 5, the reason why the SLSS resources of thesame location and number are configured in each of multiple carriersthat are set by the carrier aggregation may be for synchronizing(sidelink) logical (subframe) indexes (and/or DFNs) between the multiplecarriers.

The UE receives SLSS transmission configuration information thatindicates whether a synchronization signal (e.g., PSSS/SSSS) istransmitted actually by using the SLSS resources (step, S220). Moreparticularly, a network may indicate whether the UE perform an SLSStransmission operation actually in the corresponding SLSS resource onlyin the non-synchronization reference carrier (e.g., the carrier which isnot a synchronization reference carrier (NON-SYNRFCC) among the multiplecarriers.

The UE may transmit a synchronization signal (e.g., PSSS/SSSS) by usingthe SLSS resources indicated by the SLSS resource configurationinformation in the non-synchronization reference carrier based on theSLSS resource configuration information (step, S230). Of course, thisoperates only in the case that it is configured to transmit asynchronization signal in the non-synchronization reference carrierbased on the SLSS resource configuration information.

The SLSS resource configuration information and the SLSS transmissionconfiguration information may be received by being included in the samemessage, or received by being included in separate messages.

FIG. 7 illustrates a particular example to which the method described inFIGS. 5 and 6 is applied.

Referring to FIG. 7, a network transmits the SLSS resource configurationinformation to UE #1 (step, S310). The SLSS resource configurationinformation may setup an SLSS resource for carrier #1, 2 and 3 which iscarrier-aggregated. Here, it is assumed that carrier #2 and 3 are thenon-synchronization reference carriers. It is assumed that carrier #1 isthe synchronization reference carrier. As described above, SLSSresources of the same location and number may be setup in the multiplecarriers #1, 2 and 3 that are carrier-aggregated.

The network transmits the SLSS transmission configuration information toUE #1 (step, S320). In this case, the SLSS transmission configurationinformation may indicate or notify that an SLSS is not actuallytransmitted for carrier #2 and 3. That is, the UE may be configured withthe location of SLSS resources for carrier #2 and 3, which arenon-synchronization reference carriers, but configured not to transmitan SLSS.

Although it is not shown in FIG. 7, in the case that the networkconfigures that an SLSS is actually transmitted in carrier #2 but anSLSS is not actually transmitted in carrier #3 between carrier #2 and 3,which are non-synchronization reference carriers through the SLSStransmission configuration information, according to this, the UE maytransmit an SLSS in carrier #2 actually, but may not transmit an SLSS incarrier #3 actually.

UE #1 may transmit an SLSS to UE #2 through carrier #1 (step, S330).Carrier #1 is the synchronization reference carrier, and an SLSS may betransmitted on carrier #1 always when the synchronization resource issetup. Alternatively, even in the case that carrier #1 is thesynchronization reference carrier, a network may configure whether anSLSS is actually transmitted. In this case, the SLSS transmissionconfiguration information may include the information indicating whetherto transmit an SLSS actually even for carrier #1, which is thesynchronization reference carrier.

[Proposed method #5] In the case that there is a reserved (/selected)(transmission) resource (e.g., pattern (/location/number), period(/subframe offset), etc.) (in advance or before) on carrier # X, whenreserving (/selecting) a (transmission) resource in relation to carrier# Y, an LCAP_UE may consider (/select) (only) (partial) resource whichis overlapped with the reserved (/selected) (transmission) resource (ona time domain) on the (corresponding) carrier # X preferentially (orlimitedly).

As an example, it is configured that the maximum number of resourcesthat may be selected on the same TTI throughout multiple carriers maynot be greater than a transmission capability (TX CAPABILITY) of a UE,for example, the number of supported transmission chains and/or may belimited to the number that does not induce a POWER-LIMITED CASE. ThePOWER-LIMITED CASE may mean the case that the summation of V2X messagetransmission powers calculated for each carrier exceeds the maximumtransmission power (MAXIMUM TX POWER, e.g., 23 dBm) of the UE, in thecase that V2X message transmissions on the multiple carriers arepartially or entirely overlapped on a time domain.

In other words, when selecting a resource of a specific carrier (e.g.,carrier # Z), the UE may exclude the TTI on which the resource selectionof the corresponding maximum number is (already) completed, and(randomly) selects a resource on the remaining TTI, and then, mayperform a resource selection of other carrier on the correspondingselected TTI until it reaches to a maximum allowed number.

[Proposed method #6] The CBR (/CR) (and/or remainingtransmission/resource use opportunity in comparison with CR_LIMIT and/orsensing) measurement value on carrier # X which is preconfigured(/signaled) may be extendedly applied to other carrier (configured(/signaled) by the CA) (including carrier # X).

As an example, when the (corresponding) CBR (/CR) (and/or remainingtransmission/resource use opportunity in comparison with CR_LIMIT and/orsensing) measurement value is extendedly applied, different (weight)ratio (/part) values may be considered for each different carriers.

As another example, in the case that the location and/or number of asynchronization signal (transmission (and/or reception)) resource is(partially) differently configured (/signaled) between differentcarriers that are configured (/signaled) by the CA, through applicationof the following rules, logical indexes (/DFNs) (in relation to V2Xcommunication) may be synchronized between multiple carriers.

[Proposed method #7] As an example, a resource on carrier # Y (orcarrier # X) (partially) overlapped with a resource location of asynchronization signal in carrier # Y (or carrier # X) may be excludedwhen carrier # Y (or carrier # X) logical index (/DFN) is allocated,together with (actual) synchronization signal resource in relation tocarrier # Y (or carrier # X) or by configuring (/signaling) “RESERVEDSUBFRAME” in relation to carrier # Y (or carrier # X) (e.g., this maymean a resource to which V2X pool logical index (/DFN) is not allocated)by assuming (/regarding) the resource as (virtual) synchronizationsignal resource which is additionally configure (/signaled) to carrier #Y (or carrier # X).

As another example, when cross carrier scheduling (CCS) is performed, inorder to decrease the (time (/frequency)) synchronization difference (tothe maximum) between a transmission (and/or reception) on carrier # Xthat schedules and a transmission (and/or reception) on carrier # Y thatis scheduled, the cross carrier scheduling operation may be (limitedly)performed (/allowed) between V2X resource pools in which the samesynchronization source type based transmission (/reception) is allowedto different carriers.

As an example, in the case that the CCS related control (/scheduling)information is transmitted subframe # N of scheduling carrier # Xbelonged to V2X resource pool in which a transmission based on thesynchronization source type # A is allowed, (interlinked) datatransmission may be performed in a nearest subframe in V2X resource poolin which a transmission based on the synchronization source type # A isallowed on carrier # Y after 4 ms (4 subframe) from subframe # N time.

For the CA, the following cases may be supported.

1) Parallel transmission of MAC PDUs. Here, the “parallel transmission”means a transmission in different carriers, which is simultaneous ondifferent timings. In this case, the payloads of the MAC PDUs may bedifferent with each other. 2) Parallel transmission of replicas of thesame packet. 3) Capability improvement in an aspect of a receiver. Inthe aspect of a receiver, a simultaneous reception in multiple carriersmay be assumed. In an aspect of a transmitter, a transmission may occurthrough carriers corresponding to subset among usable carriers. A UE maysupport an operation of transmission through a single carrier and alsosupport an operation of reception through multiple carriers.

A PSCCH and an associated PSSCH may be transmitted through the samecarrier. However, this does not mean exclusion that a PSCCH includesinformation of other carrier.

In a UE aspect, in the case that a synchronization source isindependently selected in different carriers, a synchronization signalsubframe may be different in the carriers, and accordingly, DFN numbers,subframe boundaries, and the like may also become different among thecarriers.

In the case that the subframe boundary is the same but DFN numbers aredifferent, location of resources that should be deferred semi-staticallyin the carriers may be shifted gradually. Then, a simultaneoustransmission occurs in a certain subframe and an individual transmissionoccurs in other subframe, and accordingly, fluctuation of transmissionpower may occur. When a transmission power is fluctuated, a sensingoperation at a receiver may be unstable.

Furthermore, in the case that subframe boundary is different betweencarriers, it is hard to utilize a transmission power thoroughly.

In summary, 1) in a UE aspect, when an independent synchronizationsource is selected between carriers, synchronization signal subframesmay become different among the carriers, and as a result, the DFNnumbers and the subframe boundaries may become changed in the carriers.2) When DFN numbers are not arranged, even in the case that a UE detersresource sets in the carriers, the location of resource that should bedeferred semi-statically in the carriers may be shifted. 3) When thesubframe boundaries become different, it is hard to utilize atransmission power thoroughly.

In order to prevent an occurrence of the problems, it may be required todetermine a sidelink synchronization anchor carrier. The sidelinksynchronization anchor carrier may also be represented as thesynchronization reference carrier described above.

With respect to a group of the sidelink component carriers (CCs), acommon synchronization source priority configuration may be used.PSCCH/PSSCH transmission on an arbitrary sidelink CC in the group may beperformed based on the synchronization reference which is selected forthe sidelink synchronization anchor carrier, and SLSS/PSBCH should beperformed based on the synchronization reference of the sidelinksynchronization anchor carrier.

When a UE select a synchronization source in the sidelinksynchronization anchor carrier, for the synchronization procedure of theexisting UEs, the same SLSS/PSBCH are required to be transmitted to allCCs in the sidelink CC group.

In the case that there are only UEs operating by LTE-Rel-15, for thepower efficiency, the SLSS/PSBCH may be transmitted only on the sidelinksynchronization anchor carrier. There may be a plurality of sidelinksynchronization anchor carriers in different services or localboundaries.

The number of asynchronous CCs transmitted/received simultaneously maybe dependent upon a UE capability.

<Proposal 1> Definition of Sidelink Synchronization Anchor Carrier

With respect to a group of sidelink CCs, a common synchronization sourcepriority configuration may be used. The synchronization referenceselected for the sidelink synchronization anchor carrier may be used forPSCCH/PSSCH transmission on an arbitrary CC in the group. The SLSS/PSBCHtransmission should be transmitted based on the synchronizationreference selected in the sidelink synchronization anchor carrier. Withrespect to a group of sidelink CCs, subframe boundaries and DFN numbermay be aligned.

As another example, in the case that an actual its own transmission(chain) capability is smaller than the number of transmission carriers(TX CARRIERs) selected in a higher layer (e.g., APPLICATION LAYER)(e.g., the UE may be interpreted as a UE of limited transmissioncapability), the UE may select a specific carrier (e.g., anchor carrier,synchronization reference carrier, the highest priority carrier, etc.)which is preconfigured (/signaled) for use of the synchronization signaltransmission. And/or the UE may randomly select among transmissioncarriers selected in a higher layer (e.g., APPLICATION LAYER), and/ormay select a transmission carrier selected in a higher layer (e.g.,APPLICATION LAYER) by interleaving in a time domain according to apredefined rule. And/or the UE may select a carrier on which theexisting UE (LEGACY UE) is not existed and/or exclude the carrier onwhich only a service of an advanced UE (UE operating in accordance withLTE REL-15) is allowed and select the remaining carriers.

As another example, in the case that V2X message transmissions arepartially or entirely overlapped in a time domain on multiple carriers,and/or the summation of V2X message transmission powers calculated foreach carrier exceeds the maximum transmission power (MAXIMUM TX POWER,e.g., 23 dBm) of the UE (this case is referred to as POWER-LIMITEDCASE), the UE may omit V2X message transmission on a part of carriersand/or decrease the power of V2X message transmission.

Example #1

V2X message transmission of relatively low (or lower than a thresholdvalue which is preconfigured (/signaled) PPPP (and/or service priorityand/or carrier priority) (or relatively higher (/lower)) (or higher thana threshold value which is preconfigured (/signaled)) CBR (/CR) level(and/or remaining transmission/resource use opportunity in comparisonwith CR_LIMIT) is omitted (and/or transmission power is decreased), butan application of the corresponding transmission omitting operation(and/or transmission power decreasing operation) may be performed untilthe POWER-LIMITED CASE is relieved.

As a particular example, it is assumed that V2X message PPPP values oncarriers #1/2/3 are PPPP # A/B/C, respectively, and the priority amongthe corresponding PPPPs is A>B>C. In the case that a UE may get out ofthe POWER-LIMITED CASE when V2X message transmission on carrier #3 ofthe lowest PPPP value is omitted (and/or the power is decreased),without the omission of the V2X message transmission on carrier #2(and/or decrease of power), the V2X message transmission on theremaining carrier #1/2 may be maintained.

Example #2

In the case that Example #1 is applied, and in the case that a part ofV2X message transmissions of the same priority (e.g., in the case thatPPPP, service priority, carrier priority, carrier CBR (/CR) level,remaining transmission/resource use opportunity in comparison withCR_LIMIT, resource PSSCH-RSRP (/S-RSSI) is the same) should be omitted(and/or transmission power should be decreased) in order to get out ofthe POWER-LIMITED CASE, (A) the UE may randomly select V2X message toomit (and/or to decrease the transmission power). And/or (B) the UE mayomit the V2X message on carrier of relatively higher (/lower) (or higher(/lower) than a threshold value which is preconfigured (/signaled)) CBR(/CR) (and/or remaining transmission/resource use opportunity incomparison with CR_LIMIT) value (and/or decrease the transmissionpower). And/or (C) the UE may omit a periodic (or aperiodic) messagetransmission preferentially than aperiodic (or periodic) messagetransmission (and/or decrease the transmission power) and/or (D) the UEmay perform (all) transmissions without the omission (and/or decrease ofthe transmission power), exceptionally.

Example #3

The count information of the available count of omitting transmissionconsecutively (and/or decreasing power) for each priority (e.g., PPPP,service priority, carrier priority, carrier CBR (/CR) level, remainingtransmission/resource use opportunity in comparison with CR_LIMIT,resource PSSCH-RSRP (/S-RSSI)) may be preconfigured (/signaled) from anetwork (or an eNB). In the case that the corresponding rule is applied,the problem that the V2X message transmission of relatively low priorityis excessively omitted (or transmission is excessively decreased) may bealleviated.

As another example, according to the following (partial or entire)rules, (excessive) overlapping of a resource (re)selection on multiplecarriers may be avoided (and/or HALF-DUPLEX problem may be alleviated(simultaneously)).

The corresponding rule may be limitedly applied to (A) the case that aUE should transmit V2X message on carriers which is configured(/signaled) by a higher layer of which capability is relatively greaterthan its own transmission (chain) capability (and/or in the case ofsecuring a transmission chain switching time (between differentcarriers) and performing resource selection considering it), (B) thecase of avoiding the POWER-LIMITED CASE, (C) the case of alleviatingHALF DUPLEX problem in relation to INTRA-BAND CA, and the like.

A resource selection in relation to a specific carrier in the presentinvention may be limitedly or additionally performed only in aselectable transmission candidate resource set which is determined by asensing operation (e.g., excluding high interference resource).

Example #1

Basically, a resource (re)selection for each carrier is randomly (orindependently) performed in an order which is preconfigured (/signaled).However, after the number (this is referred to as NUM_OV) of overlappingcarrier(s) resources for TTI of which selection is completed before iscounted, in the case that the NUM_OV on TTI satisfies a predefinedcondition, the corresponding TTI may be excluded from the resourceselection for the corresponding specific carrier, and randomly selectedamong the resource on the remaining TTI.

The UE may also randomly select the resource on the TTI of relativelysmaller (or greater) NUM_OV value among the remaining TTI(s) that arenot excluded.

The condition may be defined as below. Here, for example, when resourceis (re)selected on a specific carrier, the K number of TTIs (e.g., K=1)which is in front of and/or behind the carrier(s) resource(s) of whichselection is completed before may be additionally excluded (e.g., usedfor transmission chain switching time).

(1) The case that NUM_OV is the same as a transmission capability (e.g.,supported number of transmission chains) of a UE

(2) The case that the remainder of transmission power budget (TX POWERBUDGET) restriction (or the maximum transmission power of the UE)subtracted by the summation of transmission power in relation to NUM_OVis unable to allow (/support) additional simultaneous transmission (onthe corresponding TTI) without causing the POWER-LIMITED CASE.

FIG. 8 illustrates an example (option 1-1) of resource selection foreach carrier in the case that the carrier aggregation is used in V2Xtransmission.

Referring to FIG. 8, it is assumed that carriers #1, 2 and 3 areconfigured to a UE by the carrier aggregation for V2X communication andthe UE is a UE provided with only two transmission chains. That is, itis assumed that the UE has a capability of transmitting V2X signal onlyto two carriers simultaneously.

In this case, the UE may exclude a part of resources (e.g., subframes)from a candidate resource selection for V2X communication in sensingprocedure of each carrier. For example, the UE may exclude the resourceof which PSSCH-RSRP measurement value is greater than a preconfiguredthreshold value or of which S-RSSI measurement value is relatively highsimultaneously while the resource is a resource reserved by other UE.FIG. 8 exemplifies the case that the resource (e.g., subframe) isexcluded during the sensing process that subframes 1 and 2 are excludedin carrier #1, subframes 1, 3, 4 and 7 are excluded in carrier #2, andsubframes 2 and 5 are excluded in carrier #3 during the sensing process.

The UE may select a resource for V2X communication for each carrieraccording to a predefined carrier order or configured carrier order(e.g., the UE may receive V2X configuration information, and the V2Xconfiguration information may indicate to select a transmission resourcein the order of the first carrier and the second carrier). In this case,the carrier resource selection order may be defined by considering ProSepriority per packet (PPPP), CBR, and so on. For example, it is assumedthat the UE selects resource for V2X communication in the order ofcarriers #1, 2 and 3.

First, it is assumed that the UE selects subframes 3 and 6 (e.g., randomselection) among subframes that are not subframe excluded in the sensingprocess, in carrier #1. Next, the UE selects a resource for V2Xcommunication among subframes that are not subframe excluded in thesensing process, in carrier #2, and in this case, the UE considers theselected resource for V2X communication of the carrier that completesthe resource selection previously, that is, carrier #1. For example,since the transmission capability of the UE is not exceeded (i.e.,transmittable in two carriers simultaneously) even in the case that theUE selects subframe 6 in carrier #2, the UE selects subframe 6 ofcarrier #2.

Similarly, the UE may also select subframe 2 of carrier #2.

Next, the UE selects a resource for V2X communication among subframesthat are not subframe excluded in the sensing process, in carrier #3,and the UE considers the selected resources for V2X communication of thecarriers that complete the resource selection previously, that is,carrier #1 and carrier #2. For example, since the transmissioncapability of the UE is exceeded (i.e., transmittable in two carrierssimultaneously) in the case that the UE selects subframe 6 of carrier#3, the UE selects a resource for V2X communication among the remainingsubframes except subframe 6 of carrier #3. Since the transmissioncapability of the UE is not exceeded (i.e., transmittable in twocarriers simultaneously) even in the case that the UE selects subframe 3in carrier #3, the UE selects subframe 3 of carrier #3. Similarly, theUE may also select subframe 7 of carrier #3.

FIG. 9 illustrates a resource selection method performed by a UEaccording to option 1-1 described above.

Referring to FIG. 9, a UE selects a transmission resource (a firstresource) on a first carrier (step, S410). In the case that atransmission capability (Tx capability) of the UE is exceeded when aspecific subframe is used in a second carrier by considering the firstresource, the UE randomly select a resource (a second resource) on theremaining subframes except the specific subframe (step, S420).

For example, in the specific subframe, the number of transmission chainsin the UE may be less than the number of configured transmissioncarriers. Alternatively, in the specific subframe, the UE may notsupport a frequency band combination including the first resource of thefirst carrier and the third resource of the second carrier.Alternatively, the specific subframe may correspond to a transmissionchain switching time of the UE.

The UE may transmit a signal using the first resource and the secondresource (step, S430). The signal may be V2X signal. The UE may applyoption 1-1 described above to the case a) the number of transmissionchains is less than the number of configured transmission carriers, b)the UE does not support a given band combination, or c) the subframecorresponds to a transmission chain switching time.

In addition, the UE may follow option 1-2 that will be described belowin other cases (e.g., the UE fails to satisfy RF requirement due to thereason such as PSD imbalance in the subframe).

FIG. 10 illustrates another example (option 1-2) of a resource selectionfor each carrier in the case that the carrier aggregation is used in V2Xcommunication.

Referring to FIG. 10, it is assumed that carriers #1, 2 and 3 areconfigured to a UE by the carrier aggregation for V2X communication andthe UE is a UE provided with only two transmission chains. That is, itis assumed that the UE has a capability of transmitting V2X signal onlyto two carriers simultaneously.

The UE may select a resource for V2X communication for each carrieraccording to a predefined carrier order or configured carrier order. Inthis case, the carrier resource selection order may be defined byconsidering ProSe priority per packet (PPPP), CBR, and so on. As aresult, for example, it is assumed that the UE independently selectsresource for V2X communication in the order of carriers #1, 2 and 3.

First, the UE may select subframes 3 and 6 (e.g., random selection)among subframes that are not subframe excluded in the sensing process,on carrier #1. Next, the UE may randomly select a resource for V2Xcommunication among subframes that are not subframe excluded in thesensing process, in carrier #2. At this time, in the case that theresource randomly selected with respect to carrier #2 exceeds thetransmission capability of the UE itself (considering a selectedresource for V2X communication of the carrier that completes theresource selection previously), the UE may repeat the random resourceselection with respect to carrier #2 until the resource that does notexceed the transmission capability is selected. As a result, forexample, subframes 2 and 6 may be selected on carrier #2.

Next, the UE may select (e.g., randomly select) a resource for V2Xcommunication with respect to carrier #3. At this time, it is assumedthat the UE selects subframes 3 and 6 on carrier #3 (in random way). Inthis case, the selected resource does not exceed the transmissioncapability (i.e., transmittable in two carriers simultaneously) of theUE in subframe 3, but exceeds the transmission capability (i.e.,transmittable in two carriers simultaneously) of the UE in subframe 6.In this case, the UE may (randomly) reselect a resource on carrier #3until a subframe that does not exceed the transmission capability of theUE is selected. That is, the UE repeats the resource reselection oncarrier #3 until the transmission resource that the UE is supportable isselected.

According to option 1-1, when a UE selects a transmission resource on aspecific carrier, in the case that the UE selects a specific subframe inthe specific carrier and the subframe exceeds the transmissioncapability limit of the UE considering the resource reserved (selected)on other carrier, the UE (randomly) selects among the remainingsubframes except the specific subframe. According to option 1-2, when aUE selects a transmission resource on a specific carrier, in the casethat the UE selects a (random) resource (e.g., subframe) preferentiallyand the result of the corresponding resource selection exceeds thetransmission capability limit of the UE considering the resourcereserved (selected) on other carrier, the UE repeats a transmissionresource reselection (e.g., randomly) with respect to the correspondingspecific carrier until the transmission resource that the UE may supportis selected.

FIG. 11 illustrates another example (option 2) of a resource selectionfor each carrier in the case that the carrier aggregation is used in V2Xcommunication.

Referring to FIG. 11, it is assumed that carriers #1, 2 and 3 areconfigured to a UE by the carrier aggregation for V2X communication andthe UE is a UE provided with only two transmission chains. That is, itis assumed that the UE has a capability of transmitting V2X signal onlyto two carriers simultaneously. The UE may select a resource for V2Xcommunication for each carrier according to a predefined carrier orderor configured carrier order. In this case, the carrier resourceselection order may be defined by considering ProSe priority per packet(PPPP), CBR, and so on.

For example, it is assumed that the UE selects resource for V2Xcommunication in the order of carriers #1, 2 and 3. At this time, the UEmay perform a resource selection for V2X communication independently foreach carrier on each of carrier #1, 2 and 3. As a result, for example,it is assumed that the UE selects subframes 3 and 6 on carrier #1, andselects subframes 6 and 8 on carrier #2 and selects subframes 1 and 6 oncarrier #3. In this case, although subframe 6 is selected on all ofcarriers #1, 2 and 3, the UE cannot perform a transmission for threecarriers simultaneously in subframe 6 of carriers #1, 2 and 3. That is,in subframe 6, it exceeds the transmission capability (i.e.,transmittable in two carriers simultaneously) of the UE. In this case,in option 2, all of the transmissions in subframe 6 may be dropped, oronly a transmission of relatively low priority which is predefined(e.g., transmission of low PPPP or transmission of high CBR on acarrier) may be dropped so as not to exceed the transmission capabilityof the UE.

Meanwhile, the ‘limited transmission capability of a UE’ may mean thecase that a UE is unable to support (simultaneous) transmission withrespect to multiple carriers in a specific subframe owing to thefollowing reasons (a) to (d), particularly.

-   -   (a) The case that the number of transmission chain (Tx chain) of        the UE is smaller than the number of transmission carriers        configured in the subframe,    -   (b) The case that the UE does not support a given band        combination or carrier combination in the subframe,    -   (c) The case that the subframe corresponds to a transmission        chain switching time,    -   (d) The case that the UE is unable to satisfy RF requirement        owing to the reason such as power spectrum density (PSD)        imbalance in the subframe.

Option 1-1 described in FIG. 8 may be applied to cases (a), (b) and (c).With respect to case (d), in the case that it exceeds the transmissioncapability when using a certain subframe, the UE may drop thetransmission in the corresponding subframe.

Alternatively, option 1-1 is applied to cases (a), (b) and (c), and withrespect to case (d), the UE may repeat a resource reselection in acandidate resource set until a transmission resource that satisfies thetransmission capability is selected.

Alternatively, option 1-2 may be applied to cases (a), (b) and (c), andoption 2 may be applied to case (d).

Alternatively, option 1-1 may be applied to cases (a), (b), (c) and (d).

Alternatively, option 1-2 may be applied to cases (a), (b), (c) and (d).

Alternatively, option 2 may be applied to cases (a), (b), (c) and (d).

Alternatively, option 1-1 may be applied to cases (a), (b) and (c), andoption 1-2 may be applied to other cases.

Example #2

In example #1, a resource selection order among carriers may be (A)defined by a carrier priority described above which is preconfigured(/signaled) and/or (B) defined by the highest (/lowest) PPPP value of aV2X message transmitted on a carrier and/or (C) defined by a carrierindex and/or (D) defined in a descending (/or ascending) order based ona CBR (/CR) measurement (and/or remaining transmission/resource useopportunity in comparison with CR-LIMIT) value, and the like and/or (E)randomly defined and/or (F) defined to preferentially select a carrier(in the same band) (or synchronization reference (SYNCH. REFERENCE)carrier) that does not require a transmission chain switching(time/gap).

As another example, for a resource selection order among carriers, thecarrier in which a message transmission of relatively short (or long)generation (/transmission/resource reservation) period (and/or high(low) RELIABILITY REQUIREMENT and/or low (or high) LATENCY REQUIREMENTis performed may be preferentially selected.

The rule described above may be extendedly applied to the options (e.g.,option 1-1, option 1-2, etc.) described above.

Example #3

When example #1 is applied, considering a transmission chain switchingtime occurrence problem owing to a limited transmission capability(and/or half duplex problem (in relation to intra band CA)), in the casethat the number of carrier(s) resources overlapped for each TTI in whichselection is completed does not satisfy a predefined condition, theresource on the corresponding TTI (in which the resource selection isalready completed) may be selected preferentially until satisfying thepredefined condition (e.g., in a direction that carrier(s) resource(s)is selected on the same TTI to the maximum), and/or the K number of TTIsin front of and/or behind carrier(s) resource(s) in which selection iscompleted may be excluded from the resource selection for carrier (suchan excluded resource may be used for a transmission chain switchingtime).

Example #4

When example #4 is applied, in the case that there is no remaining TTIthat satisfies a predefined condition when a resource in relation to aspecific carrier is selected, (A) a V2X message transmission on thecorresponding carrier may be omitted, or (B) in the case that a V2Xmessage transmission of a value of lower than (or the same as) the PPPPin relation to a V2X message on the corresponding carrier is performedon other carrier (or a V2X message transmission is performed on thecarrier of low (or the same) value in comparison with the priority ofthe corresponding carrier, or a PPPP value in relation to a V2X messagetransmission on the corresponding carrier is higher than a preconfigured(/signaled) threshold value, or a priority of the corresponding carrieris higher than a preconfigured (/signaled) threshold value, etc.), aselection of the resource overlapped with a selected/reserved resourceon other carrier on a time axis may be allowed (e.g., in order toprevent a V2X message transmission of PPPP value which is relativelyhigh value (or a V2X message transmission on a carrier having relativelyhigh priority) being omitted. In the case that latter (B) condition isnot satisfied and it is unable to perform it, a V2X message transmissionon the corresponding carrier may be omitted.

In the case that (a part or the entire) proposed techniques of thepresent invention are applied, the following carrier resource selectionmay be performed.

With respect to a given MAC PDU, a single carrier may be provided fortransmitting it by a higher layer. In the transmission carrierselection, the following factors may be considered: 1) CBR, 2) UEcapability (e.g., the number of transmission chains, power budgetsharing capability, transmission chain retuning capability, etc.).

With respect to a given MAC PDU, a single carrier is used for atransmission of the MAC PDU and a potential retransmission. When acarrier is selected, until a resource reselection is triggered withrespect to the same sidelink process, the selected carrier is used forall MAC PDUs in the same sidelink process. However, change of atransmission chain between carriers (CCs) is not excluded for differentsidelink processes.

In mode 4 CA, a carrier selection rule and a resource selectionprocedure will be described. The transmission carrier selection may beefficiently performed by considering a load balancing and a UEcapability between carriers, and it may be prevented a negativeinfluence on an accuracy of sensing process owing to excessive dynamictransmission carrier switching.

FIG. 12 illustrates an example of a resource selection in the case thatthe CA is applied in sidelink.

Referring to FIG. 12, a UE performs a resource selection in carrier # A(a first carrier).

When the UE performs a resource selection with respect to a certaincarrier, any subframe that satisfies one of the following conditions maybe excluded from a candidate resource.

1) In the case that a count of simultaneous transmission reaches to atransmission capability of the UE in a subframe, the correspondingsubframe, 2) in the case that a remaining transmission power budget isin short of allowing an additional simultaneous transmission in thesubframe, the corresponding subframe, and 3) A subframe that should beused for a transmission chain switching time.

Such subframes are excluded from the candidate resource, and thesubframes selected for a transmission already in the steps areprioritized.

In FIG. 12, it is assumed that the UE has a transmission capability ofperforming simultaneous transmission in two carriers, and transmissionpower budget or switching time is not considered, for the convenience ofdescription.

In FIG. 12, the subframe shown in grey-color is a subframe determined tohave no usable resource through a sensing process for each carrier.

First, the UE may select subframes #4 and 7 in random selection schemein carrier # A. Next, the UE performs a resource selection in carrier #B, and in this case, subframe #7 may be selected. Since the UE has atransmission capability of performing a transmission on two carrierssimultaneously, this may be a selection within the transmissioncapability of the UE. The UE is unable to select subframe #4 in carrier# B because the corresponding subframe is excluded from a sensingprocess. Accordingly, the UE may randomly select subframe #1, forexample.

In carrier #0, the UE may select subframes #1 and 4 as a transmissionsubframe. The UE is unable to select subframe #7 in carrier # B becausethe transmission capability limit of the UE is already reached.

In a UE complexity (standard/test aspect or implementation) for reducinghalf duplex problem, a simpler method may also be considered.

In this method, first, 1) In the case that a count of simultaneoustransmission reaches to a transmission capability of the UE in asubframe, the corresponding subframe, 2) in the case that a remainingtransmission power budget is in short of allowing an additionalsimultaneous transmission in the subframe, the corresponding subfame,and the like are also excluded. Later, the UE may randomly select aresource among the remaining resources (resources that are not excludedin the sensing process for each carrier or resources that are notadditionally excluded in a series of carrier resource selectionprocedure).

For example, in the example of FIG. 12, in carrier # C, subframe 7 isexcluded, but the resource selection is not limited in subframes #1 and4. That is, another subframe (e.g., subframe 0) may be selected.

As another example, when a UE selects a transmission carrier used for aMAC PDU transmission in relation to a specific service generated in apotential transmission (/reception) carrier set provided by a higherlayer, after examining conditions in the order of 1) service type of aMAC PDU, 2) transmission capability of the UE, and 3) carrier CBR (orpriority) (e.g., it may be interpreted that a priority is configured(/signaled) among the considered conditions, when selecting atransmission carrier), and the UE may finally select a transmissioncarrier proper for it.

As another example, when (a part or the entire) proposed methods of thepresent invention are applied, a transmission chain switching operation(and/or transmission chain switching gap (/time)) may use at least oneof (A) TTI that is not configured (/signaled) by SLSS resource, (B) TTIin which resource pool bitmap is not applied (e.g., deferred subframe),(C) TTI of which transmission resource reservation (/selection) is notperformed, (D) TTI in which a message transmission (/reception) of aPPPP value higher than a preconfigured (/signaled) threshold value isnot performed, (E) TTI in which transmission is performed,preferentially or limitedly.

As another example, when (a part or the entire) proposed methods of thepresent invention are applied, in the case that a UE fails to perform areception (and/or sensing) operation on a specific TTI owing to(reception) interruption in relation to a transmission chain switchingoperation, by assuming that a resource reservation is performed based onall interval candidate values that are allowed in advance by another UEon the corresponding TTI, and an exclusion operation (and/or resource(re)selection operation) of a candidate resource (e.g., subframe) whichis overlapped (in a selection window).

As another example, when (a part or entire) proposed methods of thepresent invention are applied, a UE may perform (/trigger) atransmission resource (re)selection (/reservation) operationsimultaneously, in a unit of carrier group preconfigured (/signaled)from a network (or an eNB) (e.g., this may be interpreted as a sort of“MULTI-CARRIER SYNCHRONIZED RESOURCE (RE)SELECTION (/TRIGGERING)PROCEDURE”, and this may be referred to as MCCSYN_RESEL.).

Here, for example, a reference carrier in relation to MCCSYN_RESEL maybe defined as at least one of (A) a preconfigured (/signaled) carrierfrom a network (or an eNB), (B) an anchor (/reference) carrier inrelation to synchronization, (C) a carrier of which carrier prioritypreconfigured (/signaled) is relatively high (or low), (D) a carrier ofwhich PPPP value of a transmitted (or to be transmitted) V2X message isrelatively high (or low) (or a carrier on which a message transmissionof relatively short (or long) generation (/transmission/resourcereservation) period (and/or high (low) reliability requirement and/orlow (or high) latency requirement) is performed. (E) a carrier of whichcarrier index is relatively high (or low), (F) a carrier of which CBR(/CR) measurement (and/or remaining transmission/resource useopportunity in comparison with CR_LIMIT) value is relatively high (orlow).

As an example, it may be interpreted that the (remaining) carrier(s)belonged to the same MCCSYN_RESEL carrier group (except referencecarrier) shares resource (re)selection triggering timer (/counter) (ofreference carrier), and so on.

As another example, in the case that a resource (re)selection operationof a specific carrier belonged to the MCCSYN_RESEL carrier group istriggered, when (re)selecting a resource in relation to thecorresponding carrier, a overlapping number (this is referred to asOV_RSC) for each TTI of the remaining carrier(s) resource(s) belong tothe same MCCSYN_RESEL carrier group is counted. In the case that theOV_RSC on a specific TTI satisfies a predefined condition, thecorresponding TTI may be excluded, and resources on the remaining TTImay be randomly selected.

The corresponding condition may be defined as the case that the OV_RSCis the same as or greater than a transmission capability (e.g., thenumber of supported transmission chains) of a UE and/or the case thatthe OV_RSC induces a POWER-LIMIT CASE. As another example, theMCCSYN_RESEL carrier group may be identically configured (/signaled) tothe carrier group that shares (time/frequency) synchronization based onan (specific) anchor (/reference) carrier.

As another example, when (a part or entire) proposed methods of thepresent invention are applied, a retransmission resource in relation toa specific carrier may be selected with a TTI contiguous with an initialtransmission resource as available for a UE. Here, as an example, whenthe corresponding rule is applied, it may be alleviated that atransmission chain switching gap (/time) occurs (excessively) between aninitial transmission and a retransmission (in the case that a switchingto another transmission carrier is (inevitably) performed since a timegap (/difference) is great).

As another example, when (a part or entire) proposed methods of thepresent invention are applied, resource selections in relation todifference carriers may be performed in contiguous TTIs for a UE. Thisis, for example, designed to alleviate an occurrence of half duplexproblem/excessive transmission chain switching time (/gap).

As another example, when (a part or entire) proposed methods of thepresent invention are applied, in the case that a UE performs an actualSLSS transmission (/reception) operation in a preconfigured (/signaled)SLSS resource on a specific carrier (e.g., synchronization referencecarrier) (and/or in the case that a preconfigured (/signaled) SLSSresource is existed on a specific carrier), the K number of TTIs (e.g.,K=1) which is in front of and/or behind the corresponding SLSS resourcemay be excluded from a resource selection (/allocation) on (other)carrier (e.g., used for transmission chain switching time). In the casethat the corresponding rule is applied, (under an intra-band CAsituation) a synchronization signal transmission (/reception) operationand a PSCCH/PSSCH transmission (/reception) operation may be efficientlyperformed on different carriers. The SLSS resource may be extendedlyinterpreted to “transmission of a preconfigured (/signaled) specificchannel/signal (or a message of PPPP value which is higher than apreconfigured (/signaled) threshold value)” or “transmission ofchannel/signal on a preconfigured (/signaled) specific carrier (orchannel/signal of a carrier priority which is higher than apreconfigured (/signaled) threshold value)”.

As another example, when (a part or entire) proposed methods of thepresent invention are applied, as a resource selection order amongcarriers, a UE may perform a carrier of a (channel/signal/message)transmission in which relatively high power is required (/allocated)(and/or LONG COVERAGE REQUIREMENT) (and/or high reliability requirementand/or low latency requirement) preferentially.

In the case that the corresponding rule is applied, when allocating(/calculating) a (channel/signal/message) transmission power ondifferent carriers (under an intra-band CA situation), in the case thata (channel/signal/message) transmission power on a previously allocatedcarrier is needed to be reduced (owing to excess of MPR or PSD IMBALANCEallowance limit (considering IMD PRODUCT)), a transmission on thecorresponding carrier may be omitted (or a transmission is performed onother carrier in which a transmission power on a previously allocatedcarrier is not needed to be reduced (or does not exceed MPR or PSDIMBALANCE allowance limit).

As another example, when (a part or entire) proposed methods of thepresent invention are applied, a UE may perform a synchronization signalmonitoring (and/or transmission) operation in a preconfigured(/signaled) SLSS resource on a synchronization reference carrieraccording to a preconfigured (/signaled) rule (/pattern/ratio) (e.g.,period, subframe offset).

The corresponding synchronization signal monitoring (and/ortransmission) operation may be (A) limitedly performed only in the caseof not performing a PSCCH/PSSCH transmission operation on anon-synchronization reference carrier (NON-SYNRFCC), and/or (B) performby omitting a PSCCH/PSSCH transmission on a non-synchronizationreference carrier (NON-SYNRFCC), and/or (C) performed in a UEIMPLEMENTATION form.

As another example, when (a part or entire) proposed methods of thepresent invention are applied, a UE should exclude subframe(s) (oncarrier # X) owing to the reason such as a transmission (chain)capability limit arrival, a transmission limit case occurrence,prevention of occurrence of unable to excessive reception/monitoring dueto half duplex problem, when a UE performs resource(re)selection/reservation for specific carrier # X, and for this, it isrequired to clarify the assumption that a time/an extent of a resourcereservation of exiting other carrier(s) on which resourceselection/reservation is performed already which is maintained (orvalidated). This is because it is determined whether the sametime/frequency positioned resource is continuously used based on apreconfigured (/signaled) probability wherever a resource reselectionoperation is triggered, with respect to a selected/reserved resource ona carrier, generally. That is, on the (re)selection/reservationperforming timing in relation to carrier # X, the probabilisticdetermination for resource (location) change of the (existing) othercarrier(s) on which resource selection/reservation is already performed(and/or resource reselection/reservation operation) is not alwaysperformed/triggered together.

As a method for solving this includes, for example, (A) it is assumedthat a resource reservation on the existing different carrier(s) ismaintained (or valid) during a preconfigured (/signaled) time duration(/length) (or during infinite time (/length)), or (B) the probabilisticdetermination for (future) resource (location) change of the existingother carrier(s) is performed when (re)selection/reservation for carrier# X is performed (together or in advance) (or when performing a resourceselection/reservation of the corresponding carrier(s)), or (C) it isassumed that a resource of the existing other carrier(s) is maintained(for a time or temporarily) (e.g., virtually, it may be interpreted thatthe probabilistic determination result may maintain the existingresource (location), or (D) it is assumed that a resource reservation onthe existing other carrier(s) is maintained (or valid) until a resourcereservation counter (e.g., resource reselection/reservation is triggeredwhen a resource selection/reservation counter becomes “0”) expires (oras much as a preconfigured (/signaled) multiples of a resourcereservation counter).

As another example, a UE may select a (transmission) carrier havingremaining transmission/resource use opportunity in comparison withCR_LIMIT (e.g., CR_LIMIT value may be differently configured (/signaled)for each CBR/PPPP (from a network)) which is higher (/lower) than apreconfigured (/signaled) threshold value, for a carrier used for apacket transmission of a specific PPPP value.

Here, for example, in the case that there is a plurality of(transmission) carriers that has remaining transmission/resource useopportunity in comparison with CR_LIMIT which is higher (/lower) than acorresponding threshold value, a UE may randomly select one of these.Here, for example, the corresponding threshold value may be differentlyconfigured (/signaled) for each PPPP and/or CBR and/or carrier priorityand/or service type (/sort).

Generally, CBR (/CR) measurement operation is performed whenever(actual) initial transmission or retransmission is performed. However,for the UE that has a limited transmission capability, carriers on whichactual initial/retransmission is not performed for a while may beoccurred, and the CBR (/CR) value (in relation to the correspondingcarrier) used after switching to such a carrier is a measured valuebefore a relatively longer time (i.e., a value measured when (actual)initial transmission or retransmission is performed previously on thecorresponding carrier), and may not properly reflect a latest state(e.g., load) in relation to the corresponding carrier. In order toalleviate the corresponding problem, in the case that switchingallowance from carrier # X (e.g., carrier used for a current V2X messagetransmission) to carrier # Y (switching target carrier) is allowed onlyon the time when resource reselection/reservation of carrier # X istriggered, the CBR (/CR) measurement for carrier # Y may be(additionally) performed based on resource reselection/reservationtriggering time of carrier # X (or preconfigured (/signaled) period froma network).

As another example, in the case of a UE that has a limited transmissioncapability, the UE may perform a resource selection for a specificcarrier according to Table below. In the case that a subframe(combination) that does not satisfy a predefined condition on thecorresponding carrier(s) (e.g., subframe (combination) which is notreached to a transmission capability (/transmission limit case) is notremained (in a selection window) when selecting a resource in relationto (specific) carrier(s), according to a specific technique in the Tablebelow (e.g., option 1-2 and/or option 1-1), (A) a resource reselectionoperation may be (repeatedly or limitedly) performed as much aspreconfigured (/signaled) (maximum) count, and/or (B) a resourceselection operation (/procedure) in relation to the correspondingcarrier(s) may not be performed (/started) (or omitted) (this mayprevent a resource reselection operation for a specific carrier(s) frombeing repeated excessively (or infinitely).). Here, for example, whenlatter (B) rule is applied, it may be interpreted that the transmissionoperation in relation to the corresponding carrier(s) is omitted. TheTable below summarizes options in FIGS. 8 to 11.

TABLE 1 With respect to a given MAC PDU, a single carrier may beprovided for the transmission by a higher layer. In a transmissioncarrier selection, the following factors may be considered: 1) CBR, 2)UE capability (e.g., the number of transmission chains, power budgetsharing capability, transmission chain retuning capability, etc.). Withrespect to a given MAC PDU, a single carrier is used for a transmissionof the MAC PDU and a potential retransmission. When a carrier isselected, until a resource reselection is triggered with respect to thesame sidelink process, the selected carrier is used for all MAC PDUs inthe same sidelink process. However, change of a transmission chainbetween carriers (CCs) is not excluded for different sidelink processes.The ‘limited transmission capability’ means that a UE is unable tosupport a transmission in a subframe of carrier(s) owing to thefollowing reasons (a) to (d). (a) The case that the number oftransmission chain of the UE is smaller than the number of transmissioncarriers configured, (b) The case that the UE does not support a givenband combination, (c) The case that the subframe corresponds to atransmission chain switching time, (d) The case that the UE is unable tosatisfy RF requirement owing to the reason such as PSD imbalance. A UEthat has the limited transmission capability may operate according tothe following option for a resource selection in mode 4 CA. <Option 1-1>When a UE performs a resource selection with respect to a certaincarrier, (under a resource reservation in other carrier) in the casethat using a certain subframe exceeds the transmission capability limitof the UE, the certain subframe is excluded in a candidate resource set.The order of carrier resource selection may be determined by consideringPPPP, CBR, and the like of a transmission. <Option 1-2> When anindependent resource selection is performed for each carrier, in thecase that a transmission is caused, which exceeds a transmissioncapability of a UE, the UE may perform a resource reselection repeatedlyin a given candidate resource set until the transmission resources thatthe UE is supportable are selected. The order of carrier resourceselection may be determined by considering PPPP, CBR, and the like of atransmission. <Option 2> This is a method, after performing anindependent resource selection for each carrier; a transmission isdropped for a subframe that exceeds a transmission capability limit.Option 1-1 described above may be applied to cases (a), (b) and (c), andwith respect to case (d), in the case that using a certain subframeexceeds the transmission capability, the UE may drop of a transmissionin the certain subframe. Alternatively, option 1-1 is applied to cases(a), (b) and (c), and with respect to case (d), the UE may repeat aresource reselection in a candidate resource set until a transmissionresource that satisfies the transmission capability is selected.Alternatively, option 1-2 described above may be applied to cases (a),(b) and (c), and option 2 may be applied to case (d). Alternatively,option 1-1 may be applied to cases (a), (b), (c) and (d). Alternatively,option 1-2 may be applied to cases (a), (b), (c) and (d). Alternatively,option 2 may be applied to cases (a), (b), (c) and (d). The standard forthe CA applied in V2X may also be applied to a reception ofnon-contiguous carriers. The (b) above may include a carriercombinations as well as band combination which is not supported. In thecase that the UE having a limited transmission capability is unable tosupport a transmission through carriers, the UE may follow option 1-1for cases (a), (b) and (c), or may follow option 1-2.

As another example, when option 1-2 in Table 1 is applied, in the casethat only a part (e.g., 1) of multiple (e.g., 2) (random) selectionresources for a specific carrier exceeds a transmission capability of aUE, the UE may (A) repeat a resource reselection only for thecorresponding partial number of selection resources until a resourceselection which does not exceed the transmission capability iscompleted, or (B) repeat a resource reselection for all of multipleselection resources (in relation to the corresponding carrier) until aresource selection which does not exceed the transmission capability iscompleted.

As another example, in the case of a UE that has a limited transmissioncapability, when performing a transmission carrier switching, (RF chain)RETUNING time may be required. In order to reduce the corresponding (RFchain) RETUNING time overhead, (A) when the UE select a transmissioncarrier, the UE maintains the carrier until (after an initialtransmission) retransmission is performed (or until a preconfigured(/signaled) number (or time duration) of transmissions are performed, or(B) when the UE select a resource for a specific carrier, the UE mayexclude subframe(s) between an initial transmission of other carrier anda retransmission (or a duration during which a preconfigured (/signaled)number of transmission on other carrier is performed (or time durationof a length which is preconfigured (/signaled)). Here, for example, thelatter method (B) may be (limitedly) applied only when an intervalbetween an initial transmission and a retransmission is less than apreconfigured (/signaled) threshold value.

As another example, in the case of a UE that has a limited transmissioncapability, when performing a resource selection for a specific carrier# X, a determination of excluding subframe # N on carrier # X for theuse of (RF chain) RETUNING time (e.g., assumed as “1 subframe”) may beperformed (A) in the case that, before subframe # N of carrier # X, aresource selection (or transmission) on the number of other carrier(s)that corresponds to the number of transmission capability limits of theUE itself is performed and the latest (or the last) resource (ortransmission) on the corresponding other carrier(s) is located insubframe # N−1 (or in the case that the resource selection is notlocated before the time that requires (RF chain) RETUNING time fromsubframe # N), subframe # N is determined to be the use of (RF chain)RETUNING time, and excluded from the resource selection in relation tocarrier # X.

As a particular example, it is assumed that a UE of “the number oftransmission capability limits=2” and “the number of configuredcarriers=3”. At this time, in the case that resource selections (ortransmissions) on carrier #1 and carrier #3 are performed on subframe #N−1 and subframe # N−2, respectively, subframe # N on carrier #2 isdetermined to be the use of (RF chain) RETUNING time, and should beexcluded from the resource selection in relation to carrier # X. On theother hand, in the case that resource selections (or transmissions) oncarrier #1 and carrier #3 are performed on subframe # N−1 and subframe #N−6, respectively, the UE is able to switch from subframe # N−4 tocarrier #2, subframe # N may not be necessarily excluded from theresource selection in relation to carrier # X.

As another example, in the case that a plurality of (intra-band)carriers is configured (/signaled) by the CA, owing to the half duplexproblem (i.e., in the case of performing a transmission (or reception)operation on the timing of subframe # N on a specific carrier, it isunable to perform a reception (or transmission) operation) on the same(or partially overlapping) timing on other carrier(s)), within aselection window on a specific carrier on which resource(re)selection/reservation operation is triggered, and in the case thatpreconfigured (/signaled) number (e.g., 20% of total candidate resourcenumber in a selection window) of candidate resources is not secured (orin the case that there is no remaining candidate resources), (withoutadditional action for increasing the number of candidate resources) thetransmission resource selection operation may be performed using onlythe remaining candidate resources (or resource reselection operation istriggered by including other carrier(s) in which resourceselection/reservation is completed).

Here, as an example, in the case that a specific subframe # P is failedto be monitored/received owing to half duplex problem, and the like, itmay be assumed that (all of) candidate (transmission) resource within aselection window that may be overlapped (or collided) with a resourcemay be excluded, which is apart from subframe # P as much as one (and/orthe number of preconfigured (/signaled) count of) (candidate) resourcereservation period.

As another example, in the case that (intra-band) CA is configured(/signaled), and in the case that (transmission) resources of aplurality of carriers are overlapped on a specific subframe, atransmission power reduction in relation to a part or all carriers (forexample, a transmission coverage reduction may occur) may be inevitableowing to excess of MPR or PSD IMBALANCE allowance limit (considering IMDPRODUCT).

By considering this, V2X message transmissions of different carrier(s)(partially) overlapped in time domain may be limited to those of PPPPvalues less than a preconfigured (/signaled) threshold value.

On the contrary, a V2X message transmission having a PPPP value of thecorresponding threshold value or greater is performed on subframe # K ofa specific carrier, when a resource in relation to a V2X message (e.g.,message having a PPPP value of the corresponding threshold value orsmaller) on different carrier is selected/reserved, only the remainingsubframe(s) except the corresponding subframe # K may be (limitedly)considered (or a V2X message transmission on a specific carrier having aPPPP value of the corresponding threshold value or greater may not(partially) overlapped with a V2X message transmission resource on adifferent carrier on a time domain (or (limitedly) allowed to(partially) overlap with a V2X message transmission resource on adifferent carrier of the (maximum) number of preconfigured (/signaled)on a time domain).

As another example, an influence (e.g., LEAKAGE) due to PSD IMBALANCEbetween different (intra-band CA) carriers may be changed according to alocation (and/or number) of (scheduled) resource block, and so on.Accordingly, when a UE performs a resource selection/reservation for aspecific carrier, in the case that any one of candidate resources isunable to satisfy PSD IMBALANCE allowance limit (without transmissionpower reduction) when using any one of candidate resources on a specificsubframe in a selection window (or a preconfigured (/signaled) number ormore), the UE may (randomly) select among the remaining (candidateresources on the subframe) except the corresponding subframe.

As another example, when option 2 described in the Table is applied, inthe case that the number of selection resources in relation to aplurality of carriers on a specific TTI is greater than a transmissioncapability of the UE (and/or a transmission in relation to a pluralityof carriers on a specific TTI causes a power limit case), the UE mayomit the transmission in relation to the carrier on the correspondingTTI based on a descending (or ascending) order of the remainingtransmission/resource use opportunity in comparison with CR_LIMIT.

The omission of a transmission relation to a carrier on thecorresponding TTI may be performed until the number of selectionresources in relation to a plurality of carrier on the corresponding TTIbecomes smaller than or equal to a transmission capability of the UE(and/or a transmission relation to a plurality of carrier on thecorresponding TTI does not cause a power limit case.

As another example, when a resource selection (/reservation) for aspecific carrier is performed, together with a candidate resourceexclusion operation (e.g., a resource occupied by another UE or aresource of high interference is excluded) (in a selection window) basedon a sensing operation (e.g., S-RSSI measurement, PSSCH-RSRPmeasurement), after (additional) candidate resource exclusion operation(in a selection window) considering the transmission capability excessproblem described above (and/or reception stop occurrence problem owingto a power limit case arrival problem and/or a half duplex problemand/or a transmission chain switching problem), in the case that thereis not remaining candidate resource in the selection window (and/or inthe case that the number (e.g., 20% of the number of entire candidateresources in a selection window) of preconfigured (/signaled) candidateresources is not secured, (A) a transmission in relation to thecorresponding carrier is performed on an EXCEPTIONAL RESOURCE POOL whichis preconfigured (/signaled) (once, or during a preconfigured(/signaled) count (/time), or the number of selectable candidateresources in a selection window is secured until preconfigured(/signaled) threshold value or greater), and/or (B) a switching/resourceselection (/reservation) is performed on a carrier (e.g., may be limitedto an identical service (/priority) carrier) on which relatively manycandidate resources are existed (in a selection window), and/or (C)(including the existing carrier on which resource selection(/reservation) is completed) resource reselection may be triggered.

As another example, when (transmission) carrier selection is performed(in a preconfigured (/signaled) potential (transmission) carrier set),in the case of a specific (transmission) carrier, together with atransmission capability excess problem (in a selection window) based ona sensing operation, after (additional) candidate resource exclusionoperation (in a selection window) considering (described above) (and/orreception stop occurrence problem owing to a power limit case arrivalproblem and/or a half duplex problem and/or a transmission chainswitching problem), in the case that there is not remaining candidateresource in the selection window (and/or in the case that the number(e.g., 20% of the number of entire candidate resources in a selectionwindow) of preconfigured (/signaled) candidate resources is not secured,(A) the corresponding (TX) carrier may be excluded from a selectioncandidate, and/or (B) a priority in relation to (transmission) carrierselection may be defined based on an descending (or ascending) order ofthe remaining number of candidate resources in a selection window.

As another example, a resource selection priority between carriers onwhich a message transmission of the same PPPP (and/or service) isperformed (and/or having the same CBR and/or CR and/or remainingtransmission/resource use opportunity in comparison with CR_LIMIT) (A)may be randomly defined, or (B) may be defined in an descending (orascending) order of carrier indexes (and/or CR and/or remainingtransmission/resource use opportunity in comparison with CR_LIMIT).

As another example, when a resource selection (/reservation) for acarrier is performed, when it is determined that a specific candidateresource in a selection window has a transmission capability excessproblem (and/or reception stop occurrence problem owing to a power limitcase arrival problem and/or a half duplex problem and/or a transmissionchain switching problem) (e.g., the corresponding candidate resource is(additionally) excluded if there is such a problem), (A) only acorresponding candidate resource (time) location (subframe # N) in aselection window is considered, or (B) (as well as the correspondingcandidate resource (time) location (subframe # N), a resource (time)location(s) (e.g., subframe # (N+P) of a resource reservation period (P)of (HOP_NUM) may be considered once (or infinite count or preconfigured(signaled) count or (selected) resource reservation counter count (e.g.,when resource selection/reservation counter becomes “0”, a resourcereselection/reservation is triggered)) (based on subframe # N).

In the case that the latter (B) rule is applied, a probability that thecorresponding candidate resource undergoes the problem described abovemay be relatively decreased future. Here, for example, “HOP_NUM” may be(partially or entirely) differently configured (/signaled) according toPPPP (/service type) (and/or CBR (/CR) and/or remainingtransmission/resource use opportunity in comparison with CR_LIMIT and/orcarrier priority and/or latency (/reliability) requirement and/orwhether to (HARQ) retransmit.

As another example, in the case of a UE having limited receptioncapability (e.g., in the case that the number of reception chains issmaller than the number of configured reception carriers), a sensingoperation is not performed more than a time length threshold which ispreconfigured (/signaled) on a specific carrier owing to a carrierswitching operation, and the like, (A) a message transmission (inrelation to a specific carrier) may be omitted until a sensing result ofthe corresponding time length threshold is secured, and/or (B) aresource selection/reservation and a message transmission may beperformed (on a specific carrier) by using a limited sensing result(e.g., this may be interpreted as a sort of PARTIAL SENSING operation,and/or (C) (until a sensing result of the corresponding time lengththreshold is secured) a message transmission based on a random resourceselection may be performed (on a specific carrier), and/or (D) (until asensing result of the corresponding time length threshold is secured) apreconfigured (/signaled) exceptional resource pool may be used.

As another example, in the case that a resource selection (/reservation)for a specific carrier # X is performed, together with a candidateresource exclusion operation (in a selection window) based on a sensingoperation, in the case that a message transmission of (relatively or)higher (than a preconfigured (/signaled) threshold value) PPPP isreserved on different carrier # Y, this may be (additionally) excludedin a selection window in relation to carrier # X. Here, for example,when the corresponding rule is applied, since a message transmissionresource of (relatively) low PPPP on carrier # X is overlapped with amessage transmission resource of (relatively) high PPPP on carrier # Y(in a time domain), the problem may be alleviated that the messagetransmission of the corresponding (relatively) low PPPP is omitted orthe power is reduced.

As another example, in the case that a physical layer (PHY LAYER)forwards remaining candidate resource (information) (in a selectionwindow) to a MAC layer after performing (additional) candidate resourceexclusion operation (this is referred to as EXC_PRC # B) (in a selectionwindow) considering a transmission capability excess problem (and/orreception stop occurrence problem owing to a power limit case arrivalproblem and/or a half duplex problem and/or a transmission chainswitching problem), and the like (described above) as well as acandidate resource exclusion operation (this is referred to as EXC_PRC #A) (in a selection window) based on a sensing operation, preconfigured(/signaled) “condition of securing the number of candidate resources(e.g., 20% of total number of candidate resources in a selectionwindow)” (in a selection window) in relation to (existing) EXC_PRC # Amay not be applied.

Since the examples for the proposed methods described above may also beincluded in implementation methods of the present invention, it isapparent that the examples for the proposed methods may be regarded as asort of proposed methods. In addition, the proposed methods describedabove may be independently implemented, but may also be implemented as acombination (or merge) form.

For example, although the proposed method is described on the basis of a3GPP LTE/LTE-A system for convenience of explanation, a system to whichthe proposed method is applied may also be extended to another systemother than the 3GPP LTE/LTE-A system. For example, the proposed methodsof the present invention may also be extendedly applied for D2Dcommunication. Herein, the D2D communication implies that a UEcommunicates with a different UE directly by using a radio channelHerein, although the UE implies a user terminal, when a network devicesuch as an eNB transmits and/or receives a signal according to acommunication scheme between UEs, the UE may also be regarded as a sortof the UE.

In addition, the proposed methods of the present invention may belimitedly applied only to mode 3 V2X operation (and/or mode 4 V2Xoperation).

In addition, the proposed methods of the present invention may belimitedly applied only to a preconfigured (/signaled) (specific) V2Xchannel (/signal) transmission (e.g., PSSCH (and/or (interlinked) PSCCHand/or PSBCH)).

In addition, the proposed methods of the present invention may belimitedly applied only to the case that a PSSCH and a (interlinked)PSCCH are adjacently (and/or non-adjacently) transmitted (on a frequencydomain) (and/or a transmission based on a preconfigured (/signaled) MCS(and/or coding rate and/or resource block) (value (/range)) isperformed).

In addition, the proposed methods of the present invention may belimitedly applied only to mode #3 (and/or mode #4) V2X carrier (and/or(mode #4 (/3) sidelink (/uplink) SPS (and/or sidelink (/uplink) dynamicscheduling) carrier).

In addition, the proposed methods of the present invention may be(limitedly) applied only to the case that a synchronization signal(transmission (and/or reception)) resource location and/or the number(and/or subframe location in relation to V2X resource pool and/or thenumber (and/or sub channel size and/or the number) are identical (and/or(partially) different).

In addition, the proposed methods of the present invention may beextendedly applied when a UE having a transmission (chain) capabilitywhich is smaller than the number of transmission carriers (configured bya higher layer) (re)selects a resource for each carrier as well as a UEof limited capability.

FIG. 13 is a block diagram of an apparatus in which the embodiment ofthe present invention is implemented.

Referring to FIG. 13, an apparatus 1000 includes a processor 1100, amemory 1200 and a transceiver 1300. The processor implements a proposedfunction, process and/or method. The apparatus 1000 may be a UE or aneNB. The transceiver 1300 is connected with the processor 1100 andtransmits/receives a radio signal. The memory 1200 may store informationrequired for an operation of the processor 1100, and may also store atransmission/reception signal.

FIG. 14 illustrates an example of configuring a processor 1100.

Referring to FIG. 14, the processor 1100 may include a resourceselection module 1101 and a suitability determination module 1102. Theresource selection module 1101 may select a transmission resource for aV2X signal transmission for each carrier. The suitability determinationmodule 1102 may include a CP remove module for removing a cyclic prefix(CP) from a reception signal, a Phase Rotation module for rotating aphase, a Fast Fourier Transform (FFT) module, a channel estimation (CE)module, a single input multiple output (SIMO) decoder, an inversediscrete Fourier transform (IDFT) module, a log-likelihood ratio (LLR)calculation module, a de-scrambling module, a decoder chain, and so on.

The processor may comprise an application-specific integrated circuit(ASIC), other chipset, logic circuitry and/or data processing device.The memory may include read-only memory (ROM), random access memory(RAM), flash memory, memory cards, storage media, and/or other storagedevices. The RF unit may include a baseband circuit for processing theradio signal. When the embodiment is implemented in software, theabove-described techniques may be implemented with modules (processes,functions, and so on) that perform the functions described above. Themodule may be stored in the memory and may be executed by the processor.The memory may be internal or external to the processor, and may becoupled to the processor by various well known means.

The invention claimed is:
 1. A method for transmitting avehicle-to-everything (V2X) signal performed by a user equipment (UE)having a limited transmission capability in a multi-carrier system, themethod comprising: selecting a first resource in a first carrier; basedon the use of a specific subframe in a second carrier exceeding atransmission capability of the UE considering the first resource,randomly selecting a second resource that includes one or moresubframes, excluding the specific subframe, in the second carrier; andtransmitting the V2X signal using the first resource and the secondresource, wherein the selection of the first resource in the firstcarrier prior to the selection of the second resource in the secondcarrier is based on an ordering of the first carrier and the secondcarrier, and wherein the ordering of the first carrier and the secondcarrier is determined based on a ProSe priority per packet (PPPP) of theV2X signal and a channel busy ratio (CBR).
 2. The method of claim 1,wherein a number of transmission carriers that the UE supports issmaller than a number of configured transmission carriers in thespecific subframe.
 3. The method of claim 1, wherein the UE does notsupport a frequency band combination including the first resource of thefirst carrier and the second resource of the second carrier.
 4. Themethod of claim 1, wherein the specific subframe corresponds to atransmission chain switching time of the UE.
 5. The method of claim 1,further comprising: receiving V2X configuration information, wherein theV2X configuration information indicates that a transmission resource isselected in an order of the first carrier and the second carrier.
 6. Themethod of claim 1, wherein the first carrier and the second carrier areconfigured to the UE by carrier aggregation.
 7. The method of claim 1,wherein the ordering of the first carrier and the second carrier isbased on a ProSe Per Packet Priority (PPPP) value of the V2X signaltransmitted on the first carrier and the second carrier.
 8. The methodof claim 1, wherein the ordering of the first carrier and the secondcarrier is based on a carrier priority.
 9. The method of claim 1,wherein the ordering of the first carrier and the second carrier isbased on a carrier index.
 10. The method of claim 1, wherein theordering of the first carrier and the second carrier is based on acarrier bit rate (CBR) measurement.
 11. A user equipment (UE)comprising: a transceiver configured to transmit and receive a radiosignal; and a processor operated in connection with the transceiver,wherein the processor is configured to: select a first resource in afirst carrier; based on the use of a specific subframe in a secondcarrier exceeding a transmission capability of the UE considering thefirst resource, randomly select a second resource that includes one ormore subframes, excluding the specific subframe, in the second carrier;and transmit the V2X signal using the first resource and the secondresource, wherein the selection of the first resource in the firstcarrier prior to the selection of the second resource in the secondcarrier is based on an ordering of the first carrier and the secondcarrier, and wherein the ordering of the first carrier and the secondcarrier is determined based on a ProSe priority per packet (PPPP) of theV2X signal and a channel busy ratio (CBR).
 12. The UE of claim 11,wherein a number of transmission carriers that the UE supports issmaller than a number of configured transmission carriers in thespecific subframe.
 13. The UE of claim 11, wherein the UE does notsupport a frequency band combination including the first resource of thefirst carrier and the second resource of the second carrier.
 14. The UEof claim 11, wherein the specific subframe corresponds to a transmissionchain switching time of the UE.
 15. The UE of claim 11, wherein the UEreceives V2X configuration information, and wherein the V2Xconfiguration information indicates that a transmission resource isselected in an order of the first carrier and the second carrier. 16.The UE of claim 11, wherein the first carrier and the second carrier areconfigured to the UE by carrier aggregation.
 17. The UE of claim 11,wherein the ordering of the first carrier and the second carrier isbased on a ProSe Per Packet Priority (PPPP) value of the V2X signaltransmitted on the first carrier and the second carrier.
 18. The UE ofclaim 11, wherein the ordering of the first carrier and the secondcarrier is based on a carrier priority.
 19. The UE of claim 11, whereinthe ordering of the first carrier and the second carrier is based on acarrier index.
 20. The UE of claim 11, wherein the ordering of the firstcarrier and the second carrier is based on a carrier bit rate (CBR)measurement.